Gas turbine engines generally include a compressor having rotor and stator stages for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a turbine which includes at least one rotor and stator stage for driving the compressor. The compressor generally comprises alternating rows of rotor blades attached to the rotor and stator blades, known as vanes, fixed with respect to the case. The compressor compresses the air that goes to the combustor where a portion is used to burn the fuel which in turn heats the remaining air and combustion products and flows it to the turbine. The turbine then extracts useful energy from the working fluid to power the compressor, accessories, and fan if applicable. The turbine generally comprises at least one alternating row of rotor blades attached to the rotor and stator blades, known as vanes, fixed with respect to the case. The turbine rotor blades are connected to the rotor and located aft of the combustor and within the gas flowpath so as to extract useful energy from the gas flow. In order to optimize the amount of energy extracted, arrays of vanes circumferentially positioned and radially mounted between inner and outer shrouds are interosed between the turbine blades. However, due to geometric characteristics of the vanes, large pressure gradients exist in the channels between the individual vanes. These gradients exist in the circumferential direction due to the blade surface velocity differential and in the radial direction with respect to the engine centerline due to flow vorticity. As a result of these large pressure gradients, higher pressure boundary air located along the inner surfaces of the vane endwalls, enters and disrupts the smooth aerodynamic mainstream airflow passing through the turbine. These disturbances can be large and create losses in proportion to the size of the pressure gradients that produce them.
In the past, various techniques have been proposed to overcome this problem. One such proposal was to lean the vanes in the circumferential direction. Another proposal was to flare the vanes circumferentially outward in the direction that the pressure or concave side of the vane faces. Yet another proposal was to curve the vanes so that the pressure or concave side of each vane would be turned towards the endwall casings thereby forming a "S" shaped curve. This "S" shaped curve results in a reduction in the circumferential pressure gradients thereby limiting the potential for low momentum, high pressure air to flow from the high pressure side of the channel towards the low pressure side and into the mainstream airflow. Although this curved vane is effective for reducing the circumferential pressure gradient, it significantly increases the pressure gradient in the radial direction.